image: In order to understand the origin and acceleration of cosmic ray protons, researchers used data from the Fermi Gamma-ray Space Telescope and targeted W44 and IC 443, two supernova remnants thousands of light years away. Both turned out to be strong sources of gamma rays, but not at energies below what neutral pion decay would produce -- the observational proof scientists had been looking for. This image relates to a paper that appeared in the Feb. 15, 2013, issue of Science, published by AAAS. The paper, by M. Ackermann at Deutsches Elektronen Synchrotron (DESY) in Zeuthen, Germany, and colleagues was titled, “Detection of the Characteristic Pion-Decay Signature in Supernova Remnants.” view more
Credit: [Image courtesy of NASA/DOE/Fermi LAT Collaboration]